From the Guidelines
The patient should be scheduled for a follow-up ultrasound at 32 weeks to reassess placental position, as the placenta may migrate away from the cervical os as the uterus grows, and current evidence suggests that asymptomatic patients with placenta previa may undergo weekly or biweekly US cervical length and placental edge thickness measurements to predict antepartum bleeding and need for early cesarean delivery 1. At this 20-week stage, no immediate intervention is needed. The patient should avoid sexual intercourse, vaginal examinations, and strenuous activity to reduce the risk of bleeding.
- The patient should be educated about warning signs requiring immediate medical attention, including vaginal bleeding, contractions, or pelvic pain.
- If placenta previa persists at term, a cesarean delivery will be necessary to prevent potentially life-threatening hemorrhage during vaginal delivery, as supported by the American College of Radiology recommendations for placenta accreta spectrum disorder 1. The current breech presentation is not concerning at 20 weeks as most fetuses will spontaneously convert to cephalic presentation by term.
- The normal cervical length of 4.2 cm is reassuring against preterm birth risk, according to the guidelines for placenta accreta spectrum 1. The patient's elevated BMI (32 kg/m²) should be noted, but her blood pressure is normal, and her previous uncomplicated pregnancies are favorable prognostic factors. The optimal timing for delivery in cases of placenta accreta spectrum remains unclear, but a decision analysis suggests that 34 weeks of gestation is optimal, and a window of 34 0/7-35 6/7 weeks of gestation is suggested as the preferred gestational age for scheduled cesarean delivery or hysterectomy absent extenuating circumstances in a stable patient 1.
From the Research
Patient Presentation and Ultrasound Findings
- The patient is a 39-year-old woman, gravida 3 para 2, at 20 weeks gestation with a history of in vitro fertilization and normal preimplantation genetic testing.
- The patient has no symptoms of pelvic pain, leakage of fluid, or vaginal bleeding, and fetal movement has been normal.
- Ultrasound findings show a single fetus in breech presentation, a placenta covering the internal cervical os, and a cervical length of 4.2 cm.
Placenta Previa Diagnosis and Management
- Placenta previa is a condition where the placenta covers the internal cervical os, which can cause bleeding and other complications 2.
- The diagnosis of placenta previa is typically made during routine second-trimester ultrasound, and the majority of cases resolve before term 2.
- Key risk factors for placenta previa include prior cesarean delivery, advanced maternal age, and smoking 2.
- When placenta previa is diagnosed, it is essential to assess for associated conditions like placenta accreta and vasa previa 2.
- A planned cesarean delivery is recommended in cases that persist into the late third trimester 2.
Timing of Antenatal Corticosteroids
- Administrating a single course of antenatal corticosteroids to women at risk of preterm birth between 24 and 34 weeks of gestation has been shown to decrease neonatal morbidity and mortality 3.
- The optimal timing for the administration of antenatal corticosteroids is within 1-7 days before birth, as the effect of antenatal corticosteroids declines 7 days after administration 3.
- Factors independently associated with delivery within 14 days from admission include complete placenta previa, severe bleeding at presentation, uterine contractions at presentation, and cervical length <25 mm at presentation 3.
Guidelines for Diagnosis and Management
- The Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends that women with placenta previa or low-lying placenta be managed in hospital or as an outpatient, and that cesarean delivery be performed preterm or at term, or that a trial of labour be allowed when a diagnosis of placenta previa or low-lying placenta is suspected or confirmed 4.
- Women with placenta previa or low-lying placenta are at increased risk of maternal, fetal, and postnatal adverse outcomes, including preterm delivery and postpartum hemorrhage 4, 5.
Optimal Gestational Age for Delivery
- A decision-analytic model comparing total maternal and neonatal quality-adjusted life years for delivery of women with placenta previa at gestational ages from 34 to 38 weeks found that delivery at 36 weeks, 48 hours after steroids, optimizes maternal and neonatal outcomes 6.
- Steroid administration at 35 weeks and 5 days followed by delivery at 36 weeks for women with placenta previa also optimizes maternal and neonatal outcomes 6.